Two shows debuting Tuesday night show that the networks have quickly learned how to vary a successful theme.

It may have taken television types years to start shaking up the sitcom (at least a few new comedies this fall have dropped that awful canned laughter). But when it comes to picking the bones of reality TV, they're already ahead of the curve.

Exhibits A and B: NBC's The Downer Channel and Fox's Murder in Small Town X, shows that tie themselves in knots to inject elements of real-people flavor, transparently bidding for young viewers.

For The Downer Channel, the reality juice comes from man-on-the-street interviews and video clips that are mixed up, via MTV-fast editing, with sketch comedy from a four-member troupe.

"Is it important to be funny in a different way? If it works, it is," said comic actor and executive producer Steve Martin, who started his career as a writer on the Smothers Brothers Show and The Glenn Campbell Goodtime Hour.

Along with a cast of four regulars (including Chris Rock Show co-star Wanda Sykes), special guests including Fred Willard, Terri Garr and Steven Wright help Martin poke fun at modern life's "downers," such as telephone customer service lines with endless wait times and hair comb-overs that seem to reach over to the next guy's balding pate.

But don't expect Jackass-style stunts or insults. "We actually pride ourselves that the show isn't mean," Martin said in a interview Thursday with TV critics. "It makes me cringe when I see mean things on television."

The Downer Channel's skits are hit and miss. Airing over the summer, it feels suspiciously like a back-door burnoff of a series few expect to succeed.

Not so with Murder in Small Town X, a murder-mystery-meets-reality series that took a production of Truman Show-size proportions to pull off.

Producers took over the town of Eastport, Maine, (pop. 836) for 30 days this spring, turning it into Sunrise, a fictional town stalked by a fictional murderer. Into that manufactured reality they dropped 10 real people, empowered to act as "investigators," working to uncover the murderer before they're killed themselves.

Nearly 50 actors were employed to bring Sunrise to life for the players, one of whom wins $250,000 by unmasking the killer. Since the sincerest form of imitation is television, the murder scenes are filmed in a jerky, Blair Witch Project style to heighten tension.

Through a set of rules too confusing to detail, players are introduced to clues by Los Angeles cop-turned-investigator Gary Fredo and encouraged to interview the actors-as-characters. At the end of each episode, two players are sent to different locations; one finds a crucial clue, the other is killed by the "murderer."

Critics scoffed at players who seemed to believe they were in real danger, but producers insisted their responses were reasonable.

"We're creating a context where you place people in and behavior happens," said producer George Verschoor, a veteran of MTV's The Real World and Fear. "We don't know what that behavior is going to become. But I do believe in that situation you get genuine terror."

Whatever. Fredo's presence only underscores the control producers exert, introducing clues and helping the team interpret them. It helps remove any sense that participants are truly free to play the game without interference. Once again, the reality of reality TV seems less than genuine.